The performance of an engine at wide-open throttle is often judged by the breathing characteristics of induction, intake and exhaust systems. Tuning and ramping effects at mid and high engine speeds assist air motion through the engine's air intake manifold and into engine cylinders. By utilizing the so-called inertia effect of intake gas, the volumetric efficiency of an internal combustion engine can be improved whereby the output power of the engine can be enhanced. The intake inertia effect depends upon the length of the intake passage of the engine and the engine speed. Particularly, as the engine speed is increased, the length of the intake passage at which the inertia effect is maximized becomes short. Thus, there have been proposed intake devices in which the effective length of the intake passage can be varied according to engine speed. However, many conventional intake manifold systems are still based on a fixed runner length. In such case, a manifold designer has to choose a length for the best tradeoff between engine torque and power. With a fixed runner length, the engine performance is only optimized at one RPM.
The present invention provides an air intake manifold that allows for engine performance to be optimized based on engine speed by adjusting the manifold runner lengths to achieve the best tradeoff between engine torque and power at various speeds.